The goal of the proposed research is to understand the differences in the visual mechanism which underly the differences in the color vision of normal and congenitally color deficient human observers. Psychophysical experiments using themethodologies of color matching, flicker photometric matching, and selective chromatic adaptation are designed to test hypotheses about the nature of the mechanisms which underly these individual differences. Experiments on the additivity of color matches are also proposed to determine whether additivity laws hold strictly in normal observers and to further understanding of the clear failures in the additivity of color matches which have been observed in some women heterozygous for color deficiency. The proposed research should have direct significance for theories about the mechanisms of color vision as well as indirect impact in the fields of colorimetry, clinical psychophysical testing, and genetics.